Sulphuric acid concentration



May 2, 1933.

S. A. MONTGOMERY El AL,

SULPHURI C AC ID CONCENTRATION Filed Oct. 24, 1929 Weak Ac/d d0--/00 "FTHeair Afmaspher/c Pressure Pedu c/hg Vale/e F015? Siaye Vacuum 00/106"fra/ar E6 "of Mercury 722 Secmd fiiqge Co /c 6/1 ira fa/ azmaeZ627770712" ome dohrz @ha 0a B/wu. K,B azg Patented May 2, 1933 NITD PAT

SAMUEL A. MONTGOMERY AND JOHN A. HUBBARD, or wool) RIVER, ILLInoIs, As-SIGNOR-S T0 STANDARD OIL COMPANY (INDIANA), or cnrcAGo, ILLINOIS, A003-- PORATION OF INDIANA SULPHURIC ACID CONCENTRATION Application filedOctober 24, 1929.

This invention pertains to a sulphuric acid concentration system and itrelates more particularly to the method of heating sulphuric acid for avacuum concentrator.

The object of our invention is to increase the capacity and theefficiency of commercial sulphuric acid concentrators, particularly ofthe Simonson-Mantius type.

A further object is to provide a vacuum concentration system forsulphuric acid in which the heating is effected under atmosphericpressure so that ordinary lead pipe heating coils may be used and thedanger from small leaks or weak spots in said coils is minimized.

A further object is to provide an improved method of heating the firststage of a vacuum concentrator to keep the acid constantly above itsboiling temperature, thereby avoiding periods of idleness or slowevaporation.

Our invention maybe briefly characterized as a system in which weaksulphuric acid is preheated under atmospheric pressure to a temperaturewhich will cause the acid to boil when it is introduced into the vacuumconcentrator. When the acid is passed through a reducing valve into theevaporator it immediately boils without foaming and drives off a largeamount of diluent water. Heretofore cold acid has been charged into theconcentrator and until this acid reached the boiling point the powerrequired for maintaining the vacuum was largely wasted. The heater inthe vacuum concentrator had to be very strong and free from minute leaksor weak spots because it was important that the vacuum remainunimpaired. e avoid periods of idleness in the evaporator and the use ofexpensive heating coils by preheating the sulphuric acid in a separatereceptacle which is maintained under normal pressure.

Our invention will be better understood from the accompanying drawingwhich diagrammatically illustrates a preferred embodiment.

In the process of treating mineral oils a large amount of weak sulphuricacid, about 30 B. is formed. Before this acid can be used for furthertreatment it must be con- Serial No. 402,056.

centrated to a specific gravity'of about 66 B. The first step of theconcentrationhas heretofore been the introduction of theacid into thefirst stage of the vacuum concentrator where heat isapplied to raise theacid to a boiling temperature. 7 The time required for reaching theboiling temperature is usually about four or five hours after thebeginningof the run and although the vacuum is maintained during thistime it accomplishes practically nothing. After evaporation hasproceeded for eight or ten hours, additional acid is added to restorethe original level in the evaporator. This makeup. acid lowers thetemperature below the boiling point and the efficiency of the evaporatoris again impaired by a period of relative idleness.

We provide a preheater'for the weak acid as illustrated in'the drawing.The heater may consist of a lead coil through which steam maybecirculated atatmospheric pressure. -The heating coils used in the'vacuumconcentrator must meet rigid specifications but those used in ourpreheater may be of ordinary construction because both the steam and theacid bath are at substantially atmospheric pressure so that small leaksor weak spots are immaterial. The acid entering the heater is usuallyfrom 50 to 100 F. It is heated to about 150 to 200 F. at atmosphericpressure and then passed through a reducing valve to the first stage ofa vacuum concentrator which is maintained under a Vacuum of about 26inches to 27 inches of mercury. Under-this reduced pressure the liquidboils vigorously but without undue 1 foaming and a rapid evaporation isaccomplished. The acid may be continuously supplied through a reducingvalve to maintain the most effective volume in the concentrator.

The evaporation in the concentrator may be continued by heating coilsmounted therein. We may avoid however, the use of steam coils in thevacuum system by returning acid to the heater under atmospheric pressureand carrying out the heating and evaporatingsteps as illustrated in thedrawing.

lVhile we have described a preferred embodiment of our invention it isunderstood that we are not limited to the details therein set forthexcept as defined in the following claims.

We claim:

1. A continuous process for concentrating a dilute solution underreduced pressure which comprises heating the solution at normal pressureto a temperature above the boiling point of the solution at said reducedpressure, transferring said heated solution to a concentrator,maintaining a reduced pressure in said concentrator, removing aportionof said solution from said concentrator, subjecting the removed portionto increased pressure, reheating said portion to a temperature above theboiling point of the solution at said reduced pressure, and returningsaid reheated portion with additional preheated solution to saidconcentrator whereby the latent heat of evaporation is supplied by thesensible heat of said preheated and reheated solutions to maintain thesolution in the concentrator at boiling temperature.

2. The continuous method of concentrating a dilute solution underreduced pressure which comprises maintaining a body of said solutionunderreduced pressure, separately maintaining a second body of saidsolution at a higher pressure and heating said second body of solutionto a temperature above the boiling point of the solution at reducedpressure, transferring the heated solution at the higher pressure to thebody of liquid at reduced pressure to maintain the latter at atemperature above its boiling point at said reduced pressure, recyclingpart-of said low pressure solution into said high pressure solution andmaintaining substantially constant the volume of the body of solution atreduced pressure.

Signed at WVood River, Illinois, this 13th day of Sept, 1929.

JOHN A. HUBBARD.

SAMUEL A. MONTGOMERY.

